This invention relates to a method of electrolytically depositing a film of an electrochemically synthesizable functional substance such as, for example, Prussian blue useful as an electrochromic material on an electrode plate having a conductive coating film relatively high in surface resistivity.
Besides electrodeposition of metals familiar as electroplating, electrodeposition of some electrochemically synthesizable and functional substances has been put into practical use. An example of such functional substances is Prussian blue useful as an electrochromic material.
In many cases the electrode plate on which a film of an electrochromic or otherwise functional substance is to be deposited is a glass or synthetic resin plate having a conductive coating film such as, for example, a tin dioxide film. If the conductive coating film is sufficiently low in surface resistivity, viz. lower than about 3.OMEGA./cm.sup.2, electrodeposition of a desired film on that conductive film can easily be accomplished even though the electrode plate is as large as about 40 cm square. In practice, however, the surface resistivity of the conductive film on the electrode plate is usually higher than 3.OMEGA./cm.sup.2 and ranges from about 5 to about 5.OMEGA./cm.sup.2. With such a relatively high surface resistivity of the conductive coating film on the electrode plate it is difficult to obtain a desired film of uniform thickness and quality by a conventional electrodeposition method unless the effective surface area of the electrode plate is smaller than about 100 cm.sup.2.